1. Field of the Invention
This invention relates to an FET (Field Effect Transistor) bias circuit, and specifically to a highly-efficient FET bias circuit capable of overcoming static drain current variations of an FET due to temperature variations, lowering the variations of the gain and the linear characteristics of an FET due to temperature variations, as well as reducing the distributional variations of the static gain current of FETs manufactured at different portions of a silicon wafer.
2. Description of the Related Art
When designing a circuit comprising an FET (Field Effect Transistor), the following factors need to be considered: 1) the need to suppress the deterioration of the characteristics of the electronic device due to temperature variations caused by the ambient temperature and by self-heating of the FET; and 2) the need to reduce the variations of the static drain current of FETs manufactured at different portions of a silicon wafer. To compensate for these variations, conventional circuits rely on sacrificing power of the FETs by controlling the voltage at the gate wherein the necessary voltage change is determined by connecting a resistor in series with the drain or with the source and monitoring the changes in current.
In an FET device where a small signal level is required, the static drain current is generally stabilized by applying the self-biasing of the signal FET or by connecting a resistance to the source or the drain of the FET. These solutions are tolerable to the operation of the FET where the power consumption of the device is low or where the requirement for the efficiency is low. However, they do not work for large FET devices where high efficiency is required. This is because when the static drain current is stabilized by self-biasing or by a resistor connected to the source or the drain of the FET, once the resistor is connected in series, the current flowing through the resistor will certainly result in the loss of power applied to the FET.